maybe resolve negative credit bug

I haven't been able to recreate or fully understand the negative credits bug, but it sounds like it is being caused by switching from single to double when Premium is set to "Off".

This commit hopefully resolves the problem by removing the SortMenu options to switch styles if Premium is Off.  This probably makes more sense anyway than the previous logic; we wouldn't want one player sneakily stealing another player's credits by sorting in double when no one is looking.

BGAnimations/ScreenSelectMusic overlay/SortMenu/default.lua

@@ -50,10 +50,14 @@ local t = Def.ActorFrame {
 			{"SortBy", "Recent"}
 		}
 
-		if SL.Global.Gamestate.Style == "single" then
-			table.insert(wheel_options, {"ChangeStyle", "Double"})
-		elseif SL.Global.Gamestate.Style == "double" then
-			table.insert(wheel_options, {"ChangeStyle", "Single"})
+		-- Allow players to switch from single to double and single to double
+		-- but only present these options if Joint Double or Joint Premium is enabled
+		if PREFSMAN:GetPreference("Premium") ~= "Off" then
+			if SL.Global.Gamestate.Style == "single" then
+				table.insert(wheel_options, {"ChangeStyle", "Double"})
+			elseif SL.Global.Gamestate.Style == "double" then
+				table.insert(wheel_options, {"ChangeStyle", "Single"})
+			end
 		end